1. Technical Field
The present invention relates to a medium accommodation cassette that accommodates a medium. The invention also relates to a medium feeding device that feeds a medium and a recording apparatus including the medium feeding device.
2. Related Art
In recording apparatuses represented by a facsimile machine, a printer and so on, a paper cassette that is detachably mounted in the main apparatus body is provided in some case. Further, an inner wall opposed to the leading edge of paper in a paper cassette is configured of an inclined wall so as to carry out a function that separates the uppermost sheet of paper to be fed from the other sheets of paper to be subsequently fed in some case.
Further in such a recording apparatus, a feed roller that feeds out paper from a paper cassette is provided at one end side of a rotatable arm (a side distanced from a rotational center of the arm) (for example, JP-A-2006-117362 and Japanese Patent No. 4221609).
However, the configuration as described above has a problem in that, with the increased paper consumption, an angle formed by paper and a line connecting a contact point between the paper and the feed roller and the rotational center of the arm (hereinafter, referred to as “wedge angle”) fluctuates so that a paper feed condition becomes unstable.
In order to solve the problem mentioned above, in the feeding device described in Japanese Patent No. 4221609, two feed rollers are provided on the arm so that an appropriate feed roller to make contact with recording paper is selected and used from among those two feed rollers depending on the number of stacked sheets of recording paper. With this configuration, it is possible to suppress the wedge angle from fluctuating to a large extent due to the increased paper consumption, and to feed recording paper in a stabilized manner regardless of the number of stacked sheets of recording paper.
However, in addition to the aforementioned wedge angle, there exist factors that cause paper feed performance to fluctuate. For example, in the case where a distance from the feed roller to an inclined wall at the leading edge of the paper cassette becomes shorter with the rotation of the arm, a region where the leading edge of paper can bend becomes shorter, which generates a state in which the leading edge of paper abuts against the inclined wall and cannot proceed any further (hereinafter, this state is referred to as “non-feed lock state”). In addition, if a friction coefficient between the sheets of paper or a friction coefficient between the paper and the bottom surface of the cassette becomes larger depending on a difference in paper type, a non-feed lock state is generated as well.
Detailed description will be given below with reference to FIG. 6, which is a schematic diagram indicating factors that define a paper feed condition in a configuration such that a feed roller is supported by a rotatable arm.
In FIG. 6, symbol “E” denotes a feed roll and symbol “S1” denotes a rotational center of the arm (not shown). The feed roller E is so configured as to be able to change its position by rotating (swinging) about the rotational center S1.
Symbol “C” denotes a separation slope (inclined wall) provided at a leading edge of tray, symbol “D” denotes the upper surface of recording paper, and symbol “a” denotes an angle (open angle) formed by the separation slope C and the recording paper (bottom surface of cassette). Symbol “S2” denotes a contact point between the feed roller E and the recording paper.
Further, symbol “L” denotes a distance in the horizontal direction from the contact point S2 to the separation slope C, symbol “A” denotes a distance in the horizontal direction between the rotational center S1 and the contact point S2, symbol “B” denotes a distance in the vertical direction between the rotational center S1 and the recording paper, and symbol “r” denotes a rotational direction of the feed roller E respectively. In addition, an angle β denotes an angle (wedge angle) formed by the recording paper (bottom surface of cassette) and a line connecting the rotational center S1 and the contact point S2.
Generally speaking, since the distance L becomes shorter with the increased consumption of recording paper, a risk of occurrence of a non-feed lock state becomes higher with the increased consumption of recording paper.
In particular, once the non-feed lock state as described above has occurred caused by a large difference in friction coefficient between the sheets of paper, it is further difficult to resolve the non-feed lock state due to a wedge effect explained later. In other words, as the feed roller E exerts a feeding force F on the recording paper, the roller receives a reaction force F′ against the feeding force F from the recording paper. Accordingly, a moment M about the rotational center S1 acts on the arm supporting the feed roller E due to the reaction force F′. The moment M generates a pressing force W that presses the feel roller E to the recording paper. Accordingly, as the wedge angle β is larger, the pressing force W is larger (hereinafter, this effect is referred to as “wedge effect”), for example.
If a non-feed lock state occurs in which the leading edge of paper abuts against the separation slope C and cannot proceed any further, the reaction force F′ is increased resulting in increase in the pressing force W (increase in wedge effect). Accordingly, in the case where a non-feed lock state is caused to occur particularly due to a large friction coefficient between the sheets of paper, adhesion force between the sheets of paper is also strengthened, which will further strengthen the non-feed lock state in an undesirable manner.
If such non-feed lock state occurs, there arises a risk such that a motor that drives the feed roller is overloaded, a train of gears that transmits power from the motor to the feed roller is damaged, and so on. However, these technical issues have not necessarily been taken into consideration in the paper feeding devices described in JP-A-2006-117362 and Japanese Patent No. 4221609. In particular, once a non-feed lock state has occurred, neither of those paper feeding devices can resolve the lock state.